1. Field
Example embodiments relate to a semiconductor memory device, and more particularly, to a non-volatile memory system and a programming method thereof.
2. Description of the Related Art
A semiconductor memory device may be categorized into a volatile semiconductor memory device and a non-volatile semiconductor memory device. The volatile semiconductor memory device has a faster read and write speed, but has a disadvantage that if an external power supply is disconnected, stored contents may be cleared. On the other hand, the non-volatile semiconductor memory device preserves the stored contents, even though an external power supply may be disconnected. Thus, the non-volatile semiconductor memory device may be utilized to store contents that should be preserved regardless of the supply of a power source.
Out of the non-volatile memory, for example, flash memory can electrically and collectively erase the data stored in cells, and may be widely used in, for example, a computer and a memory card. The flash memory may be categorized into a NOR type and NAND types depending on the connection state between the cells and the bit line. The NOR type flash memory may be a memory in which two or more cell transistors are connected in parallel to a one-bit line, and may store data using a Channel Hot Electron (CHE) scheme and erase the stored data using a F-N tunneling (Fowler-Nordheim tunneling) scheme. In addition, the NAND type flash memory may be a memory in which two or more cell transistors are connected in a series to a one-bit line, and may store data and erase the stored data using an F-N tunneling scheme.
Each memory cell in the flash memory device stores one-bit data or multi-bit data. When one-bit data is stored in one memory cell, the memory cell has two threshold voltage states, e.g., threshold voltages corresponding to any one of data “1” and data “0”. On the other hand, when 2-bit data is stored in one memory cell, the memory cell has a threshold voltage corresponding to any one of four threshold voltage states. Further, when 3-bit data is stored in one memory cell, the memory cell may have a threshold voltage corresponding to any one of eight threshold voltage states. Developments have been made in various techniques that store 4-bit data or more in one memory cell.